Internal gaze to establish the centre line forms chapter three of the secret of the golden flower. After establishing the energized third eye, the practitioner should direct his gaze inward with the objective of calming one's restless mind. The first physical action to do is obvious: close one's (physical) eyes. The text suggests half closing one's eyes to the point of just able to see one's nose tip. My suggestion is that it all depends on the mental condition of the practitioner. For those who are calm enough, they can completely close their eyes for best results. For those who are easy to wonder into fantasy or easy to fall asleep, half-closing or 1/4 closing would be recommended. Needless to say, for those who are not psychological stable or can get into hallucination, they should avoid deep meditative practice altogether, for safety reason.
The second question is: gaze at what? The text is silent on this issue. A possible reason is that under different stage, a practitioner should gaze at different part of his body. In this initial stage, one should gaze at the dantian (丹田) [or called lower dantian (下丹田)]. Again, like the third eye, the dantian is not a physical element but an aperture (竅) established by subtle energy (i.e. energized). I shall leave it here, a detail discussion of the energizing process is to come during the analysis of the other text, Hui Ming Jing.
Chapter 2 of the text also talked about relation between the unconscious (or collective unconscious) 元神 and consciousness 識神. I found the analysis by Carl Jung both profound and in-depth. Interested readers should directly consult his commentary in the book "The secret of the Golden Flower" (the article also appeared in Jung's "Psychology of Eastern Religion", there, among other subjects, Jung also discussed the psychology of I-Ching).
One final point, gazing towards one's dandian also implies forming an imaginary energized (chi) centre line joining the third eye and the dantain (the 2 main chi-aperture). And the strength of which is important for subsequent meditative practice as well as for physical health (which belongs to and has to be discussed under the topic of "Tai-chi chi-kung" separately).